The man accused of killing and dismembering a journalist on board his home-made submarine just offered an explanation for the death

Peter Madsen and Kim Wall together on his home-made submarine. Reuters/Business Insider

A Danish inventor accused of killing and dismembering a female Swedish journalist on board his home-made submarine has claimed that she died when a metal hatch hit her on the head.

Peter Madsen said Kim Wall was killed in an accident aboard the UC3 Nautilus submarine, which he built himself. He offered the explanation during court testimony on Tuesday, according to the Reuters news agency.

Madsen stands accused of Wall's manslaughter (Denmark does not have a separate murder charge) and also of mutilating her corpse.

Wall was last seen alive on August 10 this year, after boarding the vessel in Copenhagen while writing an article about Madsen.

Kim Wall (left) and Peter Madsen (right). Reuters

Her body was found 11 days later after it washed up in Copenhagen harbour, missing its head and all four limbs.

Madsen was rescued not far from Copenhagen after the submarine sank. He initially claimed to have dropped Wall off safely the previous day, but later admitted she had died on board.

His testimony on Tuesday was the first time he has offered an explanation for her death. Madsen appeared in court wearing military fatigues and "a blank expression on his face," according to the AFP news agency.

Danish investigators search the coast near Copenhagen for more traces of Kim Wall. Reuters

Madsen described slipping on the submarine just before Wall was hit. According to the BBC, Madsen said he was holding up a 70kg hatch for her, but dropped it after losing his footing.

Reuters reported that Madsen told the court: "I lose my foothold and the hatch shuts. Kim had been severely hurt and was laying with an intense bleeding. There was a pool of blood where she had landed."

Police investigators earlier confirmed that they had found traces of Wall's blood on board the submarine, which they dredged up from the bottom of the sea as part of the investigation.

Madsen has denied killing Wall. He has admitted a charge of desecrating her corpse, according to AFP, but said the only abuse he inflicted upon her body was throwing it into the sea, and maintains he did not dismember her.